1. Field of the Invention
The present invention relates to an image pickup apparatus using a technology to correct chromatic aberration of magnification and distortion for obtained images.
2. Discussion of the Background
In recent years, demand for a wide-angle image pickup apparatus for a rear view monitor for cars, etc. has been increasing. However, as the angle of view widens, chromatic aberration of magnification and distortion increase. Therefore, designing an optical system combining minimal aberration is difficult, and there is a need to improve performance together with image processing.
In general, although distortion is the same for each color component of red, green and blue (RGB), chromatic aberration of magnification varies depending on the color component. In addition, distortion has a relatively large impact in comparison with chromatic aberration of magnification.
A typical image pickup apparatus using an optical system having chromatic aberration of magnification and distortion uses an aberration correcting method in which chromatic aberration of magnification and distortion are simultaneously corrected by separately converting coordinates of each color component of RGB at a later stage using red, green, and blue color signals obtained by an image pickup apparatus such as a charge coupled device (CCD) and a complementary metal-oxide semiconductor (CMOS) sensor, or in which only distortion is corrected by simultaneously converting coordinates of each color component of RGB while chromatic aberration of magnification is ignored.
The method in which chromatic aberration of magnification and distortion are simultaneously corrected by independently converting coordinates of each color component of RGB requires a memory which can independently assign addresses for RGB components, resulting in an expensive memory having 3 ports with a 3-chip structure. Furthermore, random access is required for coordinate conversion, and thus, a 3 port random access memory is required to correct chromatic aberration of magnification. Therefore, even when a typical single port exterior DRAM is used as a 3 port RAM by boosting the driving frequency of the DRAM for time sharing, the pixel rate is necessary to improve the definition and the frame rate does not increase due to access latency.
Furthermore, a memory having a large capacity such as a frame buffer to store data for one entire image is required to correct distortion.
That is, such a typical method which simultaneously corrects chromatic aberration of magnification and distortion by independent coordinate conversion for each color component of RGB needs a large capacity memory with a small latency such as an SRAM when randomly accessed or with multiple ports. However, an SRAM having a large capacity or a memory having multiple ports is extremely expensive, which significantly boosts the cost of a high definition device requiring a large capacity.
On the other hand, the method which corrects only distortion by coordinate conversion shared by each color component of RGB requires a large capacity memory but can use an inexpensive single chip structured memory such as a DRAM. However, such a method is not applicable in a case in which a wide angle of view is demanded, and because the resulting chromatic aberration of magnification is not ignorable.